This invention relates to a method of forming a body by pressing particulate material, and more specifically to a method of forming a body having a bore therein and a notch in the exterior surface thereof by isostatically pressing ceramic batch material.
In manufacturing articles from particulate materials, the raw batch material often is placed in a mold formed from a resilient material, such as an elastomer. After the mold is filled, it is sealed and isostatic pressure is applied to the exterior of the mold to press the batch material into a green body. The green body is removed from the mold, further shaped when necessary, and fired to form a finished article. This process is used for forming ceramic articles such as spark plug insulators and oxygen sensor insulators. The process is known in the prior art as illustrated, for example, in U.S. Pat. Nos. 4,097,977 and 2,152,738.
The prior art process has been suitable for making articles of many shapes. However, problems have occurred when trying to form a notch in the exterior surface of a tubular green body adjacent an end of the body. Such a notch may be desirable as a locator for a multiple terminal connector which attaches to a vehicle exhaust oxygen sensor. In order to form a tubular body, a rigid core must extend through the center of the mold cavity. If a rigid insert is placed in the mold cavity to form the notch in the exterior surface of the body, the particulate material will not pack between the insert and the core and a defective body will be produced. In order to solve this problem, a tubular body was formed without the notch and the notch was machined into the green body prior to firing. However, this process added to the cost of manufacturing the finished article.